The present invention relates to a process of quick identification of an emergency wheel, for a vehicle including an electronic control system, wherein the rotational behavior of the wheels is sensed by wheel sensors, and wherein the differences of the tire tread circumferences are determined by way of correction factors.
Electronic control systems for automotive vehicles, such as antilock control systems (ABS), traction slip control systems (TCS), systems for the electronic control of brake force distribution (EBV), etc., require (exclusively or among others) data about the rotational behavior of the individual wheels as input quantities. Even minor differences in the tire tread circumferences, caused by manufacturing tolerances, uneven wear, etc., take influence on the control. This applies to a major degree in the case of mounting a so-called emergency wheel which may be smaller or larger than the other wheels.
German patent application No. 39 15 879 teaches calculating a correction factor for each wheel of a vehicle. To compensate for different tire tread circumferences, the measured wheel speed is multiplied by the associated correction factor and made the basis for the further signal processing in the control system.
International application WO89/04783 discloses a process measuring the vehicle speed in time intervals without wheel slip. In this application, correction values are determined from deviations of the wheel speeds from the vehicle speed and, subsequently, the wheel speed of the individual vehicle wheels is corrected by way of the correction values.
German patent application No. 40 36 742 discloses a circuit for a traction slip control system with brake management or engine management which is used to improve the control function when a small spare wheel instead of a driven normal-size wheel is mounted. In this application, the rotational speed measured on the spare wheel is evaluated by a correction factor determined during stable wheel rotational behavior and is thereby conformed to the measured speed value of the second driven wheel of the same axle so that the same slip control threshold as for a normal-size wheel applies to the smaller spare wheel.
It is principally necessary that these correction factors are determined, "learnt" in steps and confirmed by the control unit at the commencement of a control operation. Short-term speed variations may be due to special driving situations, such as cornering, traction torques or brake torques, vibrations, disturbances, etc. Therefore, it takes a relatively long time until a control system of this type can detect an emergency wheel, i.e. a wheel having a noticeably different tire tread circumference, and calculate a corresponding correction value.